The present invention relates to rotating heat pipes and more particularly to air conditioning apparatus incorporating a rotary heat pipe for transferring heat from a heat source to a heat sink.
The term "heat pipe" as used herein refers to any device that transfers heat by means of evaporation and condensation of a fixed amount of fluid within a sealed cavity of any shape formed in the device. In the operation of a heat pipe, a quantity of liquid locates in the relatively hot region of the cavity (the "evaporator" region) where it absorbs heat from the cavity walls in that region causing it to evaporate. The vapor flows to the cooler region of the cavity where it gives off heat to the walls of the cavity in that region (the "condenser" region) and condenses into a relatively cool liquid. The condensed, cooled liquid is then returned to the hotter zone of the cavity to repeat the cycle.
In my invention, I provide the rotating body with an interior sealed cavity which has a certain diameter at the hotter (evaporator) end of the body tapering up to a slightly smaller diameter at the cooler (condenser) end as, for example, is shown in FIG. 1.
I locate a small inventory of liquid in the cavity and rotate the body at high speed. At high speed, the liquid inventory forms a uniform annulus at the evaporator end. Heat transferred through the evaporator portion of the body wall vaporizes some of the liquid and the vapor so formed flows toward the axis of rotation and axially toward the condenser end. Here the vapor condenses on the cooled walls and the liquid condensate is pumped back along the tapered cavity walls by the small component of centrifugal acceleration tangential or parallel to the taper of the wall (hereinafter sometimes referred to as "centrifugal pumping acceleration" or "CPA"). The speed at which I rotate the body is sufficiently great to produce a component of centrifugal acceleration in the condensate parallel to the tapered cavity wall which is in excess of 1G acceleration at essentially all points on the condenser walls, and often preferably many times greater.
Accordingly, I provide a self-contained, vapor cycle heat transfer device which returns the condensate from the condenser region to the evaporator region at a relatively high velocity even against gravity or in the absence of gravity, and which can provide heat transfer ability which is greatly improved over that of conventional heat pipes and the like.
My invention is particularly well suited to provide substantial heat transfer between two ends of rotating body having a relatively long axial dimension and a relatively small diameter, since I can generate fairly large return pumping acceleration along a very small angle slope.
The benefits of my invention are obtainable only in a vapor cycle or two-phase system, and only in such a system where the cool condensing surface is kept relatively free of liquid.
It should be noted that at horizontal attitude under the influence of gravity, the liquid in the evaporator forms a non-uniform annulus when centrifugal acceleration of the liquid just exceeds 1G. As centrifugal acceleration in the liquid approaches the relatively high levels required to produce centrifugal pumping acceleration in excess of 1G according to the present invention, the liquid annulus becomes highly uniform and the pressure of the liquid increases substantially. This provides highly efficient boiling and vaporization effects since it greatly increases the convection of vapor bubbles and liquid in the annulus, and also provides a smooth interface at relatively high heat fluxes. By contrast, when boiling occurs at 1G, the interface is distorted and turbulent and tends to disperse relatively large droplets into the vapor which reduces the heat transfer effectiveness of the system. Accordingly, a device constructed in accordance with the principles of my invention may accommodate relatively high levels of heating without causing undue surface turbulence.
Because of the tendency of centrifugal acceleration to increase convection, the denser, cooler liquid flows away from the axis and quickly displaces the less dense heated liquid near the hot evaporator wall which, in turn, flows rapidly toward the axis. This prompt movement from the evaporator wall to the interface enhances evaporation, suppresses boiling and improves the heat transport capabilities of the system as a whole.
The present invention involves use of the heat pipe in an air conditioning apparatus. The heat pipe is part of a unique air conditioner having a hollow shaft extending through a small hole in the building wall and having a rotating refrigerant compressor at the end of the shaft.
In each of the embodiments of the invention herein described, the condenser surface is preferably curved in axial cross section to provide uniform pumping acceleration.
In the embodiment of the invention claimed herein an air conditioning unit is provided comprising a tapered hollow heat pipe projecting through an opening in a building wall. The heat pipe contains an inventory of liquid including a reservoir in an evaporator region at the inside of the wall and has a condenser region at the outside of the wall. Means are provided for transferring heat from the heat pipe to the outside air to condense the vapors in the condenser region, and means are provided for compressing a gaseous refrigerant at the outer surface of the heat pipe in the evaporator region. A hollow air impeller is preferably provided to receive the refrigerant and to rotate in unison with the heat pipe.